1. Field of the Invention
The present invention relates to a method for producing an annular honeycomb body, and an annular honeycomb body. Honeycomb bodies of that type are preferably used in exhaust systems of internal combustion engines, in particular in motor vehicles, water vehicles and/or aircraft, for example as a catalyst carrier body and/or particle filter.
In many countries, the emissions of internal combustion engines must adhere to legal limit values, for example in such a way that the emitted quantity of a certain exhaust gas component may not exceed a limit value. For many of those limit values, exhaust-gas treatment is necessary. For that purpose, the exhaust gas of the internal combustion engine is, for example, conducted through a catalyst carrier body and/or a particle filter which is set up in such a way that a reduction in the proportion of the exhaust-gas component in the exhaust gas takes place. That can take place, for example, by providing a catalytically active coating, which for example includes active noble metals, on a honeycomb body.
It can be advantageous to use an annular honeycomb body, depending on the available installation space for components for exhaust-gas treatment. It can, for example, be advantageous to split up an exhaust-gas flow and subject each partial flow to a separate treatment. That can occur, for example, in such a way that a first partial flow flows through an annular, for example circular-ring-shaped first honeycomb body and a second partial flow flows through a second honeycomb body which is, for example, situated in the interior of the circular-ring-shaped first honeycomb body.
Annular carrier bodies are basically known. For example, European Patent EP 0 245 736 B1 discloses an annular honeycomb body with a plurality of layers, which run in an involute fashion, between an inner and an outer casing tube. A method for producing a honeycomb body of that type is known from European Patent EP 0 322 566 B1 in which a plurality of layers is fastened, using a complex process, to an inner tube, to one another and to an outer tube. German Published, Non-Prosecuted Patent Application DE 23 21 378 A1, corresponding to U.S. Pat. Nos. 3,857,680 and 3,890,104, discloses an annular honeycomb body which is produced from a smooth sheet metal strip that is folded and is connected to an inner and an outer casing tube. A honeycomb body of that type has an insufficient surface area, with respect to the volume and the annular cross section, which can be provided with a catalytically active substance. For example, for a given annular cross section, a relatively large-volume honeycomb body must be produced in order to provide a certain surface area, for example for a catalytically active coating. International Application No. WO 94/01661 A1, corresponding to U.S. Pat. Nos. 5,464,679; 5,608,968; and 5,785,931, in turn discloses a production method in which a smooth layer and a corrugated layer are wound in a circular ring shape, then deformed from the outside inward at least at three lines, and the resulting star-like structure is then twisted in the same direction. In order to separate corrugated layers which would otherwise bear against one another, it is proposed therein to insert at least one smooth layer section between the corrugated layers. That results in increased material expenditure.